Design of a filter system with at least two longitudinal branches that have longitudinal inductors, and a filter arrangement with at least one filter section that has at least one transverse branch interposed between the longitudinal branches and at least one adjacent filter section that directly adjoins the transverse branch.
Such a filter system, which is suitable as a low-pass filter for an ADSL diplexer, is known from the xe2x80x9cHandbook of Filter Synthesisxe2x80x9d by Anatol I. Zverev, 1967, e.g., p. 59, FIG. 2.39.
A filter system with four connections has two longitudinal branches, which are symmetrically constructed. The filter system has a plurality of filter sections connected in series. The first filter section on the input side has one longitudinal inductor per longitudinal branch. The remaining filter sections, on the input side, each have a transverse branch comprising a capacitor interposed between two coupled transverse inductors and, on the output side, one longitudinal inductor per longitudinal branch. The longitudinal inductors and the transverse inductors of each filter section are coupled with each other, i.e., the inductors consist of windings that are wound around the same magnetic core. These magnetic cores are particularly costly. For each additional filter section, two additional magnetic cores are required. The more filter sections the filter system has, the more expensive it is.
In the older German Patent Application 198 51 872.2, to increase the return loss, each longitudinal inductor is replaced by two longitudinal inductors that are connected in series and are not coupled with each other. An electrical resistor is connected in parallel to one of the longitudinal inductors. This does not substantially change the transmission characteristics, such as group delay distortion.
The object of the invention is to define a method for designing a filter system, in which the filter system has fewer magnetic cores compared to the prior art, without changing the transmission characteristics.
Embodiments and further developments of the inventive concept are set forth in the dependent claims.
The method according to the invention for designing a filter system with at least two longitudinal branches that have longitudinal inductors, at least one filter section that is provided with at least one transverse branch interposed between the longitudinal branches, and at least one adjacent filter section, which directly adjoins the transverse branch, determines the arrangement of the inductors by means of a first type of transformation characterized by the following process sections:
First, the filter section has at least one free longitudinal inductor of the first longitudinal branch, a free longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch which consists of a capacitor that is interposed between two transverse inductors that are coupled together. The adjacent filter section first has at least one free longitudinal inductor of the first longitudinal branch and a free longitudinal inductor of the second longitudinal branch coupled therewith.
Subsequently, between the transverse branch and the adjacent filter section, a preliminary longitudinal inductor and a compensation inductor compensating the same and connected in series are inserted in each longitudinal branch. The preliminary longitudinal inductors are coupled with each other and the compensation inductors are coupled with each other.
Subsequently the compensation inductors are integrated into the free longitudinal inductors of the adjacent filter section.
Afterwards, the preliminary longitudinal inductors, the free longitudinal inductors of the filter section and the transverse inductors are replaced by four end inductors coupled with each other such that an equivalent circuit diagram of the four end inductors corresponds with the circuit diagram of the preliminary longitudinal inductors, the free longitudinal inductors of the filter section and the transverse inductors.
A second type of transformation provides for the following process sections:
First, the filter section has a longitudinal inductor of the first longitudinal branch, a longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch. The adjacent filter section first has at least one longitudinal inductor of the first longitudinal branch and a longitudinal inductor of the second longitudinal branch coupled therewith.
Subsequently, the longitudinal inductors of the filter section are each replaced by a first longitudinal inductor, which forms at least one part of the free longitudinal inductor, and a second longitudinal inductor connected in series therewith, to which a resistor R is connected in parallel. Corresponding longitudinal inductors belonging to the same filter section are coupled with each other.
Then, the preliminary longitudinal inductor and the compensation inductor are inserted.
A third type of transformation provides for the following process sections:
First, the filter section has a longitudinal inductor of the first longitudinal branch, a longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch. The adjacent filter section first has at least one longitudinal inductor of the first longitudinal branch and a longitudinal inductor of the second longitudinal branch coupled therewith. Subsequently, the longitudinal inductors of the filter section and the adjacent filter section are replaced, respectively, by a first longitudinal inductor and a second longitudinal inductor connected in series therewith, to which a resistor is connected in parallel. Corresponding longitudinal inductors that belong to the same filter section are coupled with each other.
Subsequently, the first longitudinal inductors and the second longitudinal inductors of the same filter section per longitudinal branch are replaced by a new first longitudinal inductor and a new second longitudinal inductor such that the new second longitudinal inductor is connected in series with the resistor. This series connection is connected in parallel to the new first longitudinal inductor. In the same filter section, the new first longitudinal inductors of the first longitudinal branch and the second longitudinal branch are coupled with each other and the new second longitudinal inductors of the first longitudinal branch and the second longitudinal branch are coupled with each other.
Afterwards, in each longitudinal branch of the filter section, an additional preliminary longitudinal inductor and an additional compensation inductor compensating the same and forming at least a portion of the free longitudinal inductor are inserted between the parallel connection of the new first longitudinal inductor to the series connection and the adjacent filter section.
Thereafter, the additional preliminary longitudinal inductors, the new first longitudinal inductors which form an additional circuit diagram, are replaced by four longitudinal end inductors that are coupled with each other, such that an equivalent circuit diagram of the four longitudinal end inductors corresponds with the additional circuit diagram.
Then, the preliminary longitudinal inductor and the compensation inductor are inserted.
A further embodiment of the invention provides for a method in which a first capacitor electrode of the capacitor is connected with a first end inductor that is connected with the adjacent filter section and with a second end inductor,
in which the winding direction of the first inductor relative to the capacitor corresponds with the winding direction of the second end inductor relative to the capacitor,
in which a second capacitor electrode of the capacitor is connected with a third end inductor that is connected with the adjacent filter section and with, a fourth end inductor,
in which the winding direction of the first end inductor relative to the capacitor is opposite to the winding direction of the third end inductor relative to the capacitor,
in which the winding direction of the third end inductor relative to the capacitor corresponds with the winding direction of the fourth end inductor relative to the capacitor.
In addition, the method according to the invention can be further developed in that
a first capacitor electrode of the capacitor is connected with a first end inductor, which is connected with the adjacent filter section,
a second end inductor is connected with the first end inductor and with the adjacent filter section,
the winding direction of the first end inductor relative to a first reference point on the electrical connection between the first end inductor and the second end inductor is opposite to the winding direction of the second end inductor relative to the first reference point,
a second capacitor electrode of the capacitor is connected with a third end inductor, which is connected with the adjacent filter section,
a fourth end inductor is connected with the third end inductor and with the adjacent filter section,
the winding direction of the third end inductor relative to a second reference point on the electrical connection between the third end inductor and the fourth end inductor is opposite to the winding direction of the fourth end inductor relative to the second reference point,
the winding direction of the first end inductor relative to the capacitor is opposite to the winding direction of the third end inductor relative to the capacitor.
Furthermore it may be provided that
a first capacitor electrode of the capacitor is connected with a second end inductor,
in which the second end inductor is connected with a first end inductor which is connected with the adjacent filter section,
the winding direction of the first end inductor relative to a seventh reference point on the electrical connection between the first end inductor and the second end inductor is opposite to the winding direction of the second end inductor relative to the seventh reference point,
a second capacitor electrode of the capacitor is connected with a fourth end inductor,
the fourth end inductor is connected with a third end inductor which is connected with the adjacent filter section,
the winding direction of the third end inductor relative to a ninth reference point on the electrical connection between the third end inductor and the fourth end inductor is opposite to the winding direction of the fourth end inductor relative to the ninth reference point, and
the winding direction of the first end inductor relative to the capacitor is opposite to the winding direction of the third end inductor relative to the capacitor.
Another further development provides that
a first longitudinal end inductor is connected in series with the resistor of the filter section in the first longitudinal branch, and a second longitudinal end inductor is connected in parallel to this series connection,
The winding direction of the first longitudinal end inductor relative to a third reference point on the electrical connection between the first longitudinal end inductor and the second longitudinal end inductor is opposite to the winding direction of the second longitudinal end inductor relative to the third reference point,
a third longitudinal end inductor is connected in series with resistor R of the filter section in the second longitudinal branch and a fourth longitudinal end inductor is connected in parallel to this series connection,
the winding direction of the third longitudinal end inductor relative to a fourth reference point on the electrical connection is between the third longitudinal end inductor and the fourth longitudinal end inductor relative to the fourth reference point,
the winding direction of the first longitudinal end inductor relative to the transverse branch is opposite to the winding direction of the third longitudinal end inductor relative to the transverse branch.
Alternatively, it may be provided that
a first longitudinal end inductor is connected in series with a second longitudinal end inductor to which resistor R of the filter section in the first longitudinal branch is connected in parallel,
the winding direction of the first longitudinal end inductor relative to a fifth reference point on the electrical connection between the first longitudinal end inductor and the second longitudinal end inductor corresponds with the winding direction of the second longitudinal end inductor relative to the fifth reference point,
a third longitudinal end inductor with a fourth longitudinal end inductor to which the resistor of the filter section in the second longitudinal branch is connected in parallel,
the winding direction of the third longitudinal end inductor relative to a sixth reference point on the electrical connection between the third longitudinal end inductor and the fourth longitudinal end inductor corresponds with the winding direction of the fourth longitudinal end inductor relative to the sixth reference point,
the winding direction of the first longitudinal end inductor relative to the transverse branch is opposite to the winding direction of the third longitudinal end inductor relative to the transverse branch.
Another alternative is characterized in that
a second longitudinal end inductor and a resistor of the filter section in the first longitudinal branch are connected in series,
in which an electrical connection is connected in parallel to the series connection comprised of the second longitudinal end inductor and the resistor,
a first longitudinal end inductor is interposed between the adjacent filter section and the series connection comprised of the second longitudinal end inductor and the resistor,
the winding direction of the first longitudinal end inductor relative to an eighth reference point on the electrical connection between the first longitudinal end inductor and the second longitudinal end inductor corresponds with the winding direction of the second longitudinal end inductor relative to the eight reference point,
a fourth longitudinal end inductor and a resistor of the filter section in the first longitudinal branch are connected in series, in which an electrical connection is connected in parallel to the series connection comprising the fourth longitudinal end inductor and the resistor,
a third longitudinal end inductor is interposed between the adjacent filter section and the series connection comprised of the fourth longitudinal end inductor and the resistor,
the winding direction of the third longitudinal end inductor relative to a tenth reference point on the electrical connection between the third longitudinal end inductor and the fourth longitudinal end inductor corresponds with the winding direction of the fourth longitudinal end inductor relative to the tenth reference point, and
the winding direction of the first longitudinal end inductor relative to the transverse branch is opposite to the winding direction of the third longitudinal end inductor relative to the transverse branch.
Finally, one embodiment of the invention may consist in that
at least one additional filter section adjacent to the filter section is provided, and
the compensation inductor for the transformation of the additional adjacent filter section are integrated into the free longitudinal inductors of the filter section.
Accordingly, the procedure should, for example, be as follows. First, the filter section has at least one free longitudinal inductor of the first longitudinal branch, a free longitudinal inductor of the second longitudinal branch coupled therewith, and the transverse branch, which consists of a capacitor interposed between two transverse inductors which are coupled with each other. The term xe2x80x9cfree longitudinal inductorxe2x80x9d denotes a longitudinal inductor to which no additional component is connected in parallel. The adjacent filter section first has at least one free longitudinal inductor of the first longitudinal branch and a free longitudinal inductor of the second longitudinal branch coupled therewith. This initial state corresponds to a filter arrangement of the prior art. For transformation, a preliminary longitudinal inductor and a compensation inductor compensating the same and connected in series therewith are then inserted into each longitudinal branch between the transverse branch and the adjacent filter section. The preliminary inductors are coupled with each other and the compensation inductors are also coupled with each other. The circuit characteristics of the filter system thus transformed remain the same, since the preliminary longitudinal inductor is compensated by the compensation inductor. For further transformation, the compensation inductors are then integrated into the free longitudinal inductors of the adjacent filter section. Thereafter, the preliminary longitudinal inductors, the free longitudinal inductors of the filter section, and the transverse inductors are replaced by four end inductors that are coupled with each other such that an equivalent circuit diagram of the four end inductors corresponds with the circuit diagram of the preliminary longitudinal inductors, the free longitudinal inductors of the filter section and the transverse inductors.
Since the four end inductors are coupled with each other, said four end inductors consist of windings that are wound around the same magnetic core.
The described transformation makes it possible to save one magnetic core for each filter section that has a transverse branch, since the free inductors and the transverse inductors, for which the two magnetic cores are required, are transformed in such a way that only one magnetic core is required.
The described transformation is an equivalence transformation, so that the circuit characteristics of the filter configuration, such as group delay distortion and transfer function, are preserved in the transformation. A filter system designed according to the invention consequently has fewer magnetic cores compared to the prior art without any change in the circuit characteristics of the filter system.